Electrical power lines and communication lines have long been supported above ground by utility poles. Traditionally, utility poles are made from wood, steel and reinforced or prestressed concrete.
Wooden utility poles consist of a natural substance and are subject to biological attack from microorganisms, insects, mammals and birds. Wooden utility poles are also threatened natural forces such as wind, rain, ultraviolet light and lightning. To counter these threats, wooden utility poles are typically treated with various chemical agents to retard decay and degradation. The problem with the use of chemical agents is the increasingly stringent environmental regulation affecting the use of harmful chemical materials.
The structural degradation of wooden utility poles may be difficult for a utility lineman to ascertain. Degraded utility poles present unsafe climbing situations. Wooden utility poles are also highly flammable. If the wooden utility poles become water soaked, then their enhanced electrical conductivity causes a safety hazard for the utility linemen and bystanders. In contrast, utility poles made from composite pultruded material are non-conductive, corrosion resistant and resistant to other forms of biological attack.
Steel utility poles also are subject to corrosion and are conductive of electricity; in order to avoid the conductivity problem, steel utility poles must be provided with heavy insulation which increases their weight and expense. The high weight of steel utility poles makes them difficult to install. The expense of fabricating steel utility poles is quite large, particularly including the necessary insulation, and significantly more than the cost of fabricating utility poles made from composite pultruded material.
Reinforced or prestressed concrete utility poles alleviate the conductivity problem of steel utility poles and alleviate the environmental problems of wooden poles. But concrete utility poles are significantly heavier than steel or wooden utility poles and the freight cost in transporting concrete utility poles throughout the country side limits their use to areas close to the manufacturing plant where they are made.
It has been proposed to make utility poles from pultruded composite materials. Representative of this technology is U.S. Pat. No. 4,803,819 (Kelsey), the disclosure of which is incorporated herein by this reference thereto.
It is a primary object of the present invention to provide an improved design of a utility power pole system comprising a hollow primary pole having an external hexagonal cross section and an internal hexagonal cross section rotated 30.degree. relative to the external hexagonal cross section. This arrangement creates a triangular area at each corner of the primary pole to give the power pole system increased structural strength. The increased structural strength permits the use of accessories attached to the power pole by means of a cantilevered connection. The design also eliminates approximately 75% or more of the weight that would be found in a conventional wooden, steel or concrete power pole. Additionally, an external or internal concentric liner or a series of overlapping liners, each also having a hexagonal cross section, are interfit inside the primary pole to further increase the lateral bending strength of the power pole system and to increase the structural efficiency of the utility pole by means of an effective structural taper.
It is a further object of the present invention to provide an improved utility power pole system that is made by a process involving the pultrusion of glass reinforced fiber material. The material is pultruded through specially designed dies to create the primary pole and the liner in the desired cross sections. The primary pole and the liner can be pultruded in any desired length or even cut to the necessary lengths after pultrusion. The pultrusion process allows the creation of longitudinal dove tail grooves along the exterior surface of the primary pole which grooves provide a convenient means of attachment to the utility pole of any desired accessories such as cross arms used to hold the electrical wires that are supported by the utility power pole.
Another object of the present invention is to provide a convenient means to integrate the utility pole into more complex support structures such as an H-frame power pole assembly and other combinations of structures.
Another object of the present invention is to provide a means for linemen to climb the utility pole; reduce manufacturing, handling and transportation costs through reducing the weight of the utility pole; and to improve the safety, corrosion resistance and resistance to biological and environmental degradation of the utility pole.
It is an advantage of the present invention that a fiber reinforced composite material utility pole can be made which weighs 25% or less of the weight of an equivalent wooden utility pole and many times less than the weight of an equivalent reinforced concrete utility pole. This substantially reduces the shipping and handling costs for utility poles made from pultruded materials.
It is a further advantage of the present invention that the use of internal or external concentric pultruded material liners achieves a structurally tapered utility pole from elements having constant cross sections. By increasing the number and length of the various liners, the same primary utility pole can be used to achieve a structurally tapered utility pole having a substantial length and significant resistance to lateral bending forces.
It is a further advantage of the present invention that the longitudinal grooves provided in the outer surface of the utility pole allow a utility workman to climb the utility pole as well as providing a means for attaching accessory components to the utility pole. When the base of the utility pole is set in concrete, the grooves are mechanically engaged by the concrete and provide resistance to the utility pole pitching or twisting about its base.
It is a further advantage of the present invention that the composite materials used to make the utility pole are resistant to acids and bases in the soil and airborne corrosives such as salt water spray. The utility pole are also highly resistant to penetration by birds, insects and mammals and are quite resistant to attack by microorganisms such as fungi. Fire retardants can be added to the pultruded material matrix which results in a utility pole having a fire resistance superior to that of wooden utility poles. A system of external coatings, external ultraviolet absorbing fibers and ultraviolet resistant resins assures that the utility pole will have slow ultraviolet degradation which enhances the long life of the utility pole.
It is a further advantage of the present invention that the composite materials from which the pole is made provide high dielectric strength as well as arc and track resistance which allows the separation between current carrying conductors to be inches instead of the feet separations which are used in a conventional wooden utility pole assembly. The reduced separation distance allows corresponding reductions in pole height and cross member lengths. The composite materials used in the utility pole absorb little moisture other than surface wetting during rainstorms, and therefore their electrical conductivity is low under moist conditions. This eliminates the need for miles of conductors which would normally be required for lightening protection.
The outer surface of the utility pole is smooth and non-toxic which eliminates the risk to utility lineman from creosote, penta burns, rashes and slivers. The smooth outer surface prevents animals from climbing the utility pole. The surface of the utility pole can be colored and/or patterned to blend into the surrounding area so that concerns over environmental appearance can be mitigated.
It is a further advantage of the present invention that the utility pole is equipped with a conical closure on its top. The pitch of the conical closure prevents birds from perching on the utility pole. The longitudinal grooves in the surface of the utility pole cooperate with the conical top to create openings in the overhang area underneath the conical top to provide convective cooling of the interior of the utility pole.